In order to detect objects, various types of sensors are installed in machines and equipment used in many production sites. The various types of sensors include a photoelectric sensor and the like disclosed in JP2015-158999 A, for example. JP2015-158999 A exemplifies a reflection type photoelectric sensor and discloses a photoelectric sensor in which detection light emitted from a light projection element is reflected by an object and the return light is received by a light receiving element.
When the photoelectric sensor disclosed in JP2015-158999 A is installed in a machine or equipment, it is necessary to install the photoelectric sensor to be adjusted at a position at which the detection light emitted from the light projection element radiates an object. However, the detection light emitted from the light projection element is invisible for naked eyes; therefore, it is impossible to install the photoelectric sensor in a machine or equipment while checking the detection light. Further, in order to determine whether the photoelectric sensor is installed in a detection area in which an object can be detected, it is necessary to perform positioning by repeatedly detecting an object being actually moved.